The present invention relates to a helicoidal vibrating separating apparatus and its use for performing effective separation between particles in extruded form, for example, to separate extrudates according to their size, weight or their apparent density.
In this text, the word extrudate and term extruded rod shaped materials are used to denote materials having the form of small rods with an outer surface which may or may not be cylindrical. The word extrudate is used as opposed to sphere but it does not exclude materials obtained by casting or molding provided that the latter have shapes approaching those of a small rod with a more or less regular external surface as, for example, trilobate, tetralobate, twists, braids, etc.
This invention, coupled possibly with separation by sifting, enables particularly the restitution to refiners or to petrochemists of extruded batches of catalyst supports or perfectly calibrated catalysts.
The system according to the invention enables particularly the exclusion from a catalyst, of particles which are too fine and hence the elimination of these "fines" in beds that refiners place in hydrotreatment reactors which permits, after sorting, the restitution of a batch perfectly calibrated extrudates and hence which are reuseable with an efficiency equal to that of new materials. The extrudates or extruded rod shaped materials generally used here are, for example, based on alumina or silica or silica alumina.
The process, according to the invention, is particularly advantageous within the framework of reutilization of a catalyst which has already been used in refining reactions (particularly hydrotreatment). Such a catalyst can not be used as, such particularly because it is attrited and has lost its catalytic properties. It must therefore, before being reutilized, be subjected to a regeneration operation.
However in addition, in the course of the preceeding refining operations, it has been subjected to considerable mechanical stresses. It follows that the catalyst, instead of being in the form of extrudates of the same size and weight (as is the case when the catalyst new), appears after prolonged use in the form of extrudates of sizes and/or weights and/or apparent densities which are different) the apparent density manifests the fact that if the same weight of several types of extrudates are packed in different bottles, different volumes of each of the extrudate types will be obtained. In particular, the catalyst can contain by weight, up to 50% of extrudates of fine size with respect to the normal size of the extrudates used in refining. Now these very fine particles (refiners call them "fines") generally of shorter lengths, for example, about 1.5 mm (0.0015 meters) or about 3 mm (0.003 meters) according to the nature of the catalyst and the refining operation, cannot validly be reintroduced into a refining reactor if it is desired to avoid losses of charges in this reactor. At least the major part of the "fines" should therefore be removed (at least 50%, preferably at least 75% and more particularly at least 90%). Preferably, it is after elimination of the "fines" that the regeneration proper of the catalyst will follow. It is however also possible to carry out this separation operation on a regenerated catalyst.
Various methods have already been proposed for the removal of fines, in particular sifting methods, which finally are inefficient whilst being very tedious. It is, for example, impossible to eliminate by sifting fines of length smaller than 1.5 mm in a batch of extrudates of 1.5 mm diameter. The diameter of the extrudates being equal to the size of the mesh, even catalysts of length greater than 1.5 mm can pass through the mesh lengthwise.
It is an object of the invention to provide a process which enables simply and effectively the elimination of the majority of the extrudates or extruded rod shaped materials of size and/or weight and/or apparent density which are inadequate.